The present invention relates to a print medium feed device for feeding a print medium to a press drum or the like and a stencil printing machine using such a print medium feed device and, more particularly, to a print medium feed device and a stencil printing machine adapted to transfer a print medium such as a print sheet in a feed path wherein an initial transfer angle of the print medium relative to a feed tray is remarkably different from a subsequent advancing angle of the print medium relative to the press drum.
Various researches and developments have been undertaken to provide an improved paper feed device for a stencil printing machine allowing to perform multi-colored print with plural printing drums, a typical example of which is disclosed in FIG. 8 which shows a part of a structure of such a stencil printing machine. In FIG. 8, first and second printing drums 101 and 102 and a press drum 103 are rotatably supported in a frame body (not shown) such that the first and second printing drums 101 and 102 are located in close proximity to an outer periphery of the press drum 103 at positions angled at 90 degrees of a central angle of the press drum 103. Outer circumferential peripheries of the respective first and second printing drums 101 and 102 carry thereon stencil clamping bases 101a and 102a, respectively, which support thereon sheet clamping segments 101b and 102b for clamping stencil sheets (not shown) onto the stencil clamping bases 101a and 102a, respectively.
Further, screens 105 are wound on the outer circumferential peripheries of the first and second printing drums 101 and 102 in a stretched state with the use of the stencil clamping bases 101a and 102a and springs 104, with each of the screens 105 being formed of a mesh-shaped porous structure which allows printing ink to permeate. Inner press rollers 106 and 107, which serve as ink supply rollers, respectively, are located inside the screens 105 of the first and second printing drums 101 and 102, respectively, with the inner press rollers 106 and 107 being moveable between a wait position not to press the screens 105 and a press-contact position to press the screens 105. During printing operation, the inner press rollers 106 and 107 are maintained in the press-contact position, in which the screens 105 are expanded outward. Also, it is arranged such that the screen 105 of the first printing drum 101 is supplied with printing ink in a first color by the inner press roller 106 and the screen 105 of the second printing drum 102 is supplied with printing ink in a second color by the inner press roller 107. The outer circumferential periphery of the press drum 103 is provided with a print sheet clamping segment 109, for clamping a leading edge of a print sheet (print paper) 108, which clamps the leading edge of the print sheet 108 transferred from a paper feed device 110 and release the leading edge of the print sheet 108 at a position in the vicinity of an inlet portion of a sheet discharge section 111.
The paper feed device 110 is constructed of a paper feed tray 112 on which a stack of print sheets 108 are located, a pair of primary paper feed rollers 113, 113 which are held in press-contact with an uppermost print sheet 108 stacked on the paper feed tray 112, a pair of secondary paper feed rollers 114, 114 located downstream of the primary paper feed rollers 113, 113, and a pair of transfer guide members 115, 115 which function to guide the print sheet 108 in a transfer path between the pair of secondary paper feed rollers 114, 114 and the press drum 103. Rotations of the primary paper feed rollers 113, 113 allow only the uppermost print sheet 108 to be transferred from the paper feed tray 112 to the pair of secondary paper feed rollers 114, 114. The print sheet 108 is then transferred with rotations of the pair of secondary paper feed rollers 114, 114 and is fed to the press drum 103 in synchronism with rotation thereof.
Now, the stencil printing machine thus arranged operates as follows. A leading edge of a first stencil sheet, which has been made on the basis of image data in a first color of an original is clamped with the sheet clamping segment 101b of the first printing drum 101, and a leading edge of a second stencil sheet, which has been made on the basis of image data in a second color of the original, is clamped with the sheet clamping segment 102b of the second printing drum 102, with the stencil sheets being mounted onto the outer circumferential peripheries of the respective screens 105. Next, the first and second printing drums 101 and 102 and the press drum 103 are rotated in synchronism with one another in directions as shown by arrows in FIG. 8, thereby causing the print sheet 108 to be transferred between the first printing drum 101 and the press drum 103 from the paper feed device 110.
The print sheet 108 thus transferred is clamped with the print sheet clamping segment 109 of the press drum 103, allowing the print sheet to pass along the outer circumferential periphery of the press drum 103 between the first printing drum 101 and the press drum 103. During this passing step of the print sheet 108, the inner press roller 106 is brought into press-contact with the screen 105 of the first printing drum 101 which is consequently expanded outward, allowing printing ink to be transferred to the print sheet 108 to reproduce a desired image pattern with a first color through a perforated image area of the first stencil sheet. The print sheet 108, which has passed between the first printing drum 101 and the press drum 103, then passes between the second printing drum 102 and the press drum 103. During this passing step of the print sheet a 108, the inner press roller 107 is brought into press-contact with the screen 105 on the second printing drum 102 which is consequently expanded outward, allowing printing ink to be transferred to the print sheet 108 to reproduce a desired image pattern with a second color. As the sheet clamping segment 109 of the press drum 103 is rotated to a position near the inlet of the sheet discharge section 111, the sheet clamping segment 109 is released, with the released print sheet 108 being discharged to the given discharge position by the sheet discharge section 111. In this manner, two-color printing is completed.
Now, operation of the paper feed device 110 is described in detail. When the primary paper feed rollers 113, 113 are rotated, only the uppermost print sheet 108 is transferred from the stack of the print sheets on the paper feed tray 112 until the leading edge of the print sheet 108 is introduced to a position between the secondary paper feed rollers 114, 114, at which position a further transfer of the print sheet 108 is stopped. Subsequently, the secondary paper feed rollers 114, 114 are rotated in synchronism with rotation of the press drum 103, allowing the print sheet 108 to be fed to the press drum 103, while guided with a pair of transfer guide members 115, 115, at a prescribed advancing point and at a prescribed advancing angle. The print sheet 108, thus transferred to the press drum 108, is successively transferred therewith.
In the event the pair of secondary paper feed rollers 114, 114 complete their transfer cycle, rotations of the secondary paper feed rollers 114, 114 are interrupted and one of the paper feed rollers 114, 114 is shifted to a disengagement position relative to the other paper feed roller. With such a shifting movement, the print sheet 108 is transferred without encountering with difficulties.
However, due to the further studies done by the inventor of the present invention, in a printing machine such as the machine discussed above, wherein two printing drums 101, 102 are located relative to a single press drum 103, however, since the first printing drum 101 is obliquely located above an upper region of the press drum 103 and a paper feed point is located at an upstream side of the first printing drum 101 in terms of rotation of the press drum 103, an advancing transfer direction of the print sheet 108 to the press drum 103 becomes substantially in a vertical direction. On the contrary, the print sheet 108 is transferred from the paper feed tray 112 in a transfer direction which is slightly angled at approximately 20 degrees relative to a horizontal direction. It will thus be understood from the foregoing description that a paper transfer path is formed with an initial transfer angle of the print sheet 108 to be transferred from the paper feed tray 112 and a subsequent advancing transfer angle of the print sheet 108 to be fed to the press drum 103, with both angles forming a remarkably large value angled from one another. In such a paper transfer path, during transfer of the print sheet 108 with the press drum 103, since the print sheet 108 tends to extend in a straight configuration due to its resilience such that a trailing edge of the print sheet 108 is transferred through the pair of the transfer guide members 115, 115 with the trailing edge remaining in sliding contact with one of the transfer guide members, a situation is encountered such that the print sheet 108 is subjected to a relatively large back tension caused by a sliding resistance. When the print sheet 108 is transferred while subjected to the back tension, difficulties are encountered in transferring the print sheet 108 in a stable fashion, resulting in a remarkable amount of undesired paper dusts. Particularly, these difficulties become more serious in a case where the print sheet 108 has an increased resilience property.
Further, in such a printing machine wherein a rotational braking unit is employed to exert a rotational braking effect onto a shaft of an upper one of the secondary paper feed rollers 114, 114 to prevent backlash of the same, since the print sheet 108 is transferred with its trailing edge remaining in sliding contact with the upper paper feed roller 114 which is exerted with the rotational braking effect, the print sheet 108 is undesirably subjected to the relatively large back tension with resultant similar problems discussed above.
The present invention has been achieved through the above-stated studies. It is, therefore, an object of the present invention to provide a print medium feed device which can minimize a back tension, to be exerted onto a print medium during transfer thereof with a press drum, as small as possible and a stencil printing machine which employs the same.
To obtain the above-stated object, in a first aspect of the present invention, a print medium feed device is provided with: a feed tray stacking print media thereon; a primary feed roller; a pair of secondary feed rollers provided downstream to the primary feed roller in a transferring direction of the print medium, the print medium being fed to the pair of secondary feed rollers through the primary feed roller in a first transferring direction; a pair of transfer guide members provided downstream to the pair of secondary feed rollers in the transferring direction of the print medium, the print medium being fed from the pair of secondary feed rollers to a predetermined member through the transfer guide members in a second transferring direction different from the first transferring direction; and an actuating mechanism shifting one of the pair of transfer guide members between a guide position in which the one of the pair of transfer guide members and the other of the pair of transfer guide members are close to each other to allow the print medium to be guided by the pair of transfer guide members and a non-guide position in which the one of the pair of transfer guide members is remotely separated from the other of the pair of transfer guide members.
In a second aspect of the present invention, a print medium feed device is provided with: a feed tray stacking print media thereon; a primary feed roller; a pair of secondary feed rollers provided downstream to the primary feed roller in a transferring direction of the print medium, the print medium being fed to the pair of secondary feed rollers through the primary feed roller in a first transferring direction; a pair of transfer guide members provided downstream to the pair of secondary feed rollers in the transferring direction of the print medium, the print medium being fed from the pair of secondary feed rollers to a predetermined member through the transfer guide members in a second transferring direction different from the first transferring direction; a rotational braking mechanism coupled to the pair of secondary feed rollers and imparting a rotational braking effect thereto; and a releasing mechanism releasing the rotational braking effect.
Besides, a stencil printing machine of the present invention is provided with: a rotatable press drum; a plurality of printing drums rotatably supported in close proximity to the press drum; a stencil making section making stencil sheets to be mounted onto outer circumferential peripheries of the respective printing drums; a feed tray stacking print media thereon; a primary feed roller; a pair of secondary feed rollers provided downstream to the primary feed roller in a transferring direction of the print medium, the print medium being fed to the pair of secondary feed rollers through the primary feed roller in a first transferring direction; a pair of transfer guide members provided downstream to the pair of secondary feed rollers in the transferring direction of the print medium, the print medium being fed from the pair of secondary feed rollers to a predetermined member through the transfer guide members in a second transferring direction different from the first transferring direction; and an actuating mechanism shifting one of the pair of transfer guide members between a guide position in which the one of the pair of transfer guide members and the other of the pair of transfer guide members are close to each other to allow the print medium to be guided by the pair of transfer guide members and a non-guide position in which the one of the pair of transfer guide members is remotely separated from the other of the pair of transfer guide members. In such a structure, a desired image pattern is formed on the print medium by supplying ink to the respective printing drums such that the ink is transferred to the print medium through the stencil sheets of the respective printing drums.
Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.